The production of synthesis gas is conventionally carried out by partial oxidation of carbon-containing materials with oxygen or an oxygen-containing gas; in particular, air at elevated pressure and relatively high temperatures of 1000.degree. to 1600.degree. C. The carbon-containing materials used are hydrocarbons, slurries of solid carbon-containing fuels in hydrocarbons, or slurries of solid carbon-containing fuels in water, such as coal/water suspensions.
EP 95 103 B1 describes a process and a burner for the production of synthesis gas. The process is carried out with the aid of a burner system composed of three concentric tubes, each of which has a conically tapering end, and a cooling chamber in the region of the burner outlet. Thus, three mass streams are fed to the reaction. The mass stream containing the oxygen or the oxygen-containing gas is conducted through the inner and the outer zone of the burner, and the carbon-containing material--a coal/water suspension--is passed through the annular space formed by the inner and middle tubes. 1 to 20% of the total oxygen required for the partial oxidation is allotted to the inner mass flow, the remaining oxygen requirement is supplied by the outer mass flow through the annular space formed by the middle and outer tubes.
The coal/water suspension forming the middle mass stream is fed to the reactor at a pressure of 1 to 20 MPa and a velocity of 1 to 25, in particular 2 to 15, m/second; while the inner and outer gas streams are passed into the reaction zone with a velocity of 50 to 300, in particular 80 to 200, m/second.
As a result of the conical tapers of the concentrically arranged tubes, the three mass streams meet each other at an acute angle. Hence, the coal/water suspension stream, after leaving the end of the conical taper, is forced or torn apart by the inner gas stream. The suspension stream is thus horizontally deflected and does not pass into the reaction zone in free fall. As a consequence, both the mean residence time of the individual coal/water droplets and the degree of conversion are increased.
At the same time, the outer gas stream impacts the coal/water suspension broadened by the inner gas stream and produces a further mixing of gas and suspension, so that a zone of uniform distribution of gas or oxygen and very fine suspension droplets is produced. This is an essential precondition for reacting the coal/water suspension to the greatest possible extent. It has been shown that, to use hydrocarbon-containing fuels for this purpose, conditions similar to those described above in more detail in connection with coal/water suspensions, are advantageous.
The partial oxidation of the carbon-containing fuel, in particular a hydrocarbon, leads to a highly chemically reactive mixture which contains about 30% to 50% by weight of carbon monoxide, about 30% to 50% by weight of hydrogen, about 3% to 20% by weight of CO.sub.2 and unreacted steam and, in smaller quantities, also contains sulfur, iron, vanadium, nickel, sodium, chlorine, and calcium.
The material composition and the ash contents of the resulting gasification product are dependent, on the one hand, on the type of fuel and, on the other hand, on the process conditions; e.g. the amount of oxygen, the temperature established, and the pressure. The partial oxidation of hydrocarbon-containing fuels is conventionally carried out at about 1000.degree. to 1600.degree., in particular at 1200.degree. to 1600.degree. C., and at pressures of 1.0 to 15.0, in particular 2.0 to 10, preferably 3.0 to 5.0, MPa. The hydrogen contained in the synthesis gas results from the reaction of water which is fed to the partial oxidation in the liquid state and/or in the form of steam. The water required for the reaction can be introduced as a separate stream or as a mixture with other streams, for example mixed with the hydrocarbons, the oxygen or oxygen-containing gas stream. It is also possible to distribute the water, both in the liquid state and in the form of steam, among a plurality of streams. The same applies to the supply of the hydrocarbon-containing fuel and the oxygen or oxygen-containing gas. These reactants can also be fed to the reaction either separately or distributed among a plurality of streams.
As a consequence of the conditions prevailing in the partial oxidation, the burner is subjected to a considerable extent to a series of physical and chemical stresses. The high exit velocities of the mass streams, in particular the gas streams, produce vibrations which cause a high mechanical load on the burner. Moreover, the composition of the highly reactive gas mixture resulting from the partial oxidation, coupled with the high temperatures used, exposes the burner to a great extent to chemical attack. In addition, slag particles, which can be deposited in the molten state on the burner, lead to chemical reactions and erosion, thereby increasing the stress on the burner, especially near its downstream end.
In addition, the burner is exposed to thermal stress, caused by the high intensity of the thermal radiation occurring in the gasification. This thermal stress is higher in the gasification of fuels containing hydrocarbons than in the corresponding reaction of a coal/water suspension. The higher gasification temperature on the one hand, and the shorter distance between the burner and the gasification zone on the other, are responsible for this. The higher temperature is a consequence of the easier flammability of the hydrocarbon and the reduced distance results from an earlier ignition of the hydrocarbon, because of its lower ignition temperature compared to the coal/water suspension.
In continuous operation, the burner is subjected not only to vibrations and a chemical attack by the highly reactive synthesis gas, but is also subjected to erosion by slag particles and to large thermal stresses. Although high-grade materials, in particular high alloy special steels such as Incoloy and Hastelloy, are used for the part of the burner projecting into the gasification reactor, the burner has only a very limited life expectancy of only about three to four months. This is a considerable disadvantage for the operation of a modern plant for the production of synthesis gas, since the burner can only be changed when the plant is shut down. However, shutting down the synthesis gas plant requires the cooling and depressurizing of the apparatus; after the defective burner has been replaced, the plant must first be heated up again and repressurized before the production of synthesis gas can be resumed.